noun
three-quarter sleeves
Refers to sleeves that end between the elbow and the wrist, commonly seen on shirts, blouses, and jackets.
このブラウスは七分袖で、春にぴったりです。
This blouse has three-quarter sleeves and is perfect for spring.
長袖 means long sleeves that reach the wrist, whereas 七分袖 is shorter, ending mid-forearm.
Compound of 七分 (shichibu, 'seven-tenths') and 袖 (sode, 'sleeve'), referring to sleeves that are roughly seven-tenths the length of full-length sleeves.